Electronically controlled engine throttles typically employ one or two adjustable throttle plates positioned in the intake air stream to control the rate at which air flows into the engine for combustion. In a single valve system, the position of a single throttle plate is varied by an electronic control signal in response to sensor signals which indicate accelerator position and other engine operating conditions. In a series valve system, two throttle plates act together to control the quantity of air flowing to the engine, the first plate being directly controlled by the driver's movement of the accelerator pedal while the second plate is moved automatically in response to other engine conditions. Both the single and series valve systems may be adapted to provide special capabilities, such as cruise control or electronic traction control.
Single and series valve systems require electronic controllers which function differently. A controller for a single valve system must provide an output signal which is responsive to both accelerator position and sensed operating conditions, whereas the controller for a series valve system generates a signal for driving the second of two throttle plates to make further adjustment, when appropriate, to the flow rate established by the first throttle plate which is operated directly by accelerator pedal movements. The design, configuration and tuning of these two controller types is consequently quite different and the design specifications developed for one type are of little use in the development of the second type.